“It was cool. Just a great moment,” the soft-spoken LeMahieu said. “That was awesome.”

LeMahieu launched a fastball over the fence in right as the Rockies kept their 1½-game advantage over Los Angeles intact after the Dodgers beat Cincinnati earlier in the day. The Diamondbacks fell 3½ games behind in the division race. This is the latest in the season the Rockies have been alone in first place since 1995.

A night after getting his first career save, Hirano (4-3) allowed a single by Gerardo Parra off the glove of first baseman Paul Goldschmidt to begin the ninth. Charlie Blackmon bunted Parra over to second and LeMahieu followed with the walk-off homer. He was doused with water after crossing home plate as fans chanted “DJ, DJ, DJ!”

“I was just looking to drive the ball. It was a lot of fun,” LeMahieu said.

Hirano’s pitch to LeMahieu was the latest miscue by a struggling Arizona bullpen where some roles have been juggled.

“He just made a mistake,” Diamondbacks manager Torey Lovullo said. “He threw a fastball that could be taken the other way.”

Overlooked in LeMahieu’s ninth-inning theatrics was the performance of Colorado’s bullpen, which turned in five perfect innings, including two each by Chris Rusin and Scott Oberg. Wade Davis (3-6) picked up the win by pitching a flawless ninth, including two strikeouts.

That marks the first time the Rockies’ bullpen has tossed five perfect innings in franchise history, according to the team.

“Awesome the bullpen was able to do our job tonight, throw up a bunch of zeroes and give our team a chance,” Oberg said. “In this building, really anything can happen from an offensive standpoint.”

Nolan Arenado had a big night for the Rockies with two doubles, including a run-scoring one in the second, and a solo homer.

LeMahieu’s blast spoiled a solid outing by Diamondbacks starter Patrick Corbin, who allowed a season-high 10 hits, but navigated his way through trouble. He went 6 1/3 innings and allowed three runs.

The left-hander’s most crucial pitch was a slider to strike out LeMahieu with the bases loaded in the fourth.

Arizona’s bullpen bent a little in the eighth, issuing two walks, only to have reliever Archie Bradley enter with two outs and get pinch-hitter Carlos Gonzalez to roll out.

Eduardo Escobar’s homer in the third inning was his 21st of the season and sixth with the Diamondbacks since being acquired from the Minnesota Twins on July 27. Goldschmidt finished 2 for 4 with a double and extended his streak of reaching base to 48 straight road games. Alex Avila added a solo homer.

“These are tough, tough to lose under these circumstances,” Lovullo said. “It hurts.”

Since 2015, the Diamondbacks are now 17-6 against Colorado during games played in September or later — including their win in the NL wild-card contest last October.

Rockies starter Jon Gray labored on a night he didn’t have his best stuff. He lasted four innings and allowed four runs.

“I wouldn’t be smiling like this if we didn’t win the game like we did,” Gray said.

SCOREBOARD WATCHING

Asked if he watches scoreboards, manager Bud Black quipped: “It’s hard not to. We have a beautiful scoreboard out there.”

Playing right field, Gonzalez has a close-up view of the scoreboard over his shoulder.

“When we’re not winning, I go like this,” he said, turning his heard as if he was looking at the scoreboard. “Just to make sure the other team is not doing better.”

WEIGHING IN

Arenado and Trevor Story are both starting to get some mention in the NL MVP race. Gonzalez’s vote would be simple — both.

“Either way it goes, I will feel extremely happy,” he said of the possibility of a teammate winning the award.

UP NEXT

Arizona RHP Clay Buchholz (7-2, 2.01 ERA) makes his first career start at Coors Field in the finale of a four-game series with Colorado on Thursday. The Rockies will throw LHP Kyle Freeland (14-7, 2.91), who is 8-2 at home this season. The game will be an MLB Facebook Watch broadcast.